"What is that process by which food when swallowed is reduced to a fit form for assimilation, but a set of mechanical and chemical actions responding to the mechanical and chemical actions which distinguish the food? Whence it becomes manifest, that, while Life in its simplest form is the correspondence of certain inner physico-chemical actions with certain outer physico-chemical actions, each advance to a higher form of Life consists in a better preservation of this primary correspondence by the establishment of other correspondences. Divesting this conception of all superfluities, and reducing it to its most abstract shape, we see that Life is definable as the continuous adjustment of internal relations to external relations. And when we so define it, we discover that the physical and the psychial life are equally comprehended by the definition. We perceive that this, which we call intelligence, shows itself when the external relations to which the internal ones are adjusted begin to be numerous, complex, and remote in time and space; that every advance in Intelligence essentially consists in the establishment of more varied, more complete, and more involved adjustments; and that even the highest achievements of science are resolvable into mental relations of coexistence and sequence, so cooerdinated as exactly to tally with certain relations of coexistence and sequence that occur externally.... "And lastly let it be noted that what we call _truth_, guiding us to successful action and the consequent maintenance of life, is simply the accurate correspondence of subjective to objective relations; while _error_, leading to failure and therefore towards death, is the absence of such accurate correspondence. "If, then, Life in all its manifestations, inclusive of Intelligence in its highest forms, consists in the continuous adjustment of internal relations to external relations, the necessarily relative character of our knowledge becomes obvious. The simplest cognition being the establishment of some connection between subjective states, answering to some connection between objective agencies; and each successively more complex cognition being the establishment of some more involved connection of such states, answering to some more involved connection of such agencies; it is clear that the process, no matter how far it be carried, can never bring within the reach of Intelligence either the states themselves or the agencies themselves."